The invention relates to a stapler, more particularly a power operated stapler which includes a clinching anvil that may be positioned beneath the nose piece of the stapler in order to clinch the staplers driven through material and which anvil may be moved out of alignment with the nose piece of the stapler so that staples may be driven into material without being clinched. Such staplers provide the facility of attaching separate pieces to each other such as the flaps on a cardboard carton in which the staples are clinched after being driven through the flaps. At the same time, however, when the anvil is moved out of a clinched position the staples may be driven to hold two elements together such as the flap of a carton and the wood of a wooden pallet in which the staples terminate in the wood and are not clinched.